I'm now here at GitHub, so I don't know whice parts of the crash report i should attach here. Here's the whole thing:
crash-2020-12-06_16.32.37-server.txt

Gas tank did not show up in the xnet controller and crating a gas chanel craashed the game.
I used version: XNetGases-1.16.4-2.1.0. as can be seen in the crash report.
I'm not sure if it's the xnet or xnet gases that caused the crash.

Awesome, thanks so much it is appreciated!

The 1.15 version of XNet also received an update to its API. Will you also be updating the 1.15 version of this mod?

Ah, will do. Gonna port the slurry channel while I'm at it.

Alright, should be up on CurseForge now. Slurries already worked but it is not possible to extract them directly from the chemical dissolution chamber. Which is most likely a fault in mekanism itself. Just extract from adjacent gas tanks instead of directly from the machine for now.

EDIT: Someone already reported the issue here mekanism/Mekanism#6764

Looks like XNet got an update and something has changed in the API. I'll update it in a few mins.